* allow bypass of install step for those that provide their own god exec...

[sethcall]

This change allows someone to suppress the install of god from rubygems, by override node['god']['install'] = false.

It defaults to true (install from rubygems) to provide backwards compatibility with the cookbook.

Why? We provide our own god executable via a debian created using fpm (https://github.com/jordansissel/fpm).